From: Harshad Shirwadkar harshadshirwadkar@gmail.com
commit b84477d3ebb96294f87dc3161e53fa8fe22d9bfd upstream.
scale_up wakes up waiters after scaling up. But after scaling max, it should not wake up more waiters as waiters will not have anything to do. This patch fixes this by making scale_up (and also scale_down) return when threshold is reached.
This bug causes increased fdatasync latency when fdatasync and dd conv=sync are performed in parallel on 4.19 compared to 4.14. This bug was introduced during refactoring of blk-wbt code.
Fixes: a79050434b45 ("blk-rq-qos: refactor out common elements of blk-wbt") Cc: stable@vger.kernel.org Cc: Josef Bacik jbacik@fb.com Signed-off-by: Harshad Shirwadkar harshadshirwadkar@gmail.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- block/blk-rq-qos.c | 14 +++++++++----- block/blk-rq-qos.h | 4 ++-- block/blk-wbt.c | 6 ++++-- 3 files changed, 15 insertions(+), 9 deletions(-)
--- a/block/blk-rq-qos.c +++ b/block/blk-rq-qos.c @@ -148,24 +148,27 @@ bool rq_depth_calc_max_depth(struct rq_d return ret; }
-void rq_depth_scale_up(struct rq_depth *rqd) +/* Returns true on success and false if scaling up wasn't possible */ +bool rq_depth_scale_up(struct rq_depth *rqd) { /* * Hit max in previous round, stop here */ if (rqd->scaled_max) - return; + return false;
rqd->scale_step--;
rqd->scaled_max = rq_depth_calc_max_depth(rqd); + return true; }
/* * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we - * had a latency violation. + * had a latency violation. Returns true on success and returns false if + * scaling down wasn't possible. */ -void rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle) +bool rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle) { /* * Stop scaling down when we've hit the limit. This also prevents @@ -173,7 +176,7 @@ void rq_depth_scale_down(struct rq_depth * keep up. */ if (rqd->max_depth == 1) - return; + return false;
if (rqd->scale_step < 0 && hard_throttle) rqd->scale_step = 0; @@ -182,6 +185,7 @@ void rq_depth_scale_down(struct rq_depth
rqd->scaled_max = false; rq_depth_calc_max_depth(rqd); + return true; }
void rq_qos_exit(struct request_queue *q) --- a/block/blk-rq-qos.h +++ b/block/blk-rq-qos.h @@ -94,8 +94,8 @@ static inline void rq_qos_del(struct req }
bool rq_wait_inc_below(struct rq_wait *rq_wait, unsigned int limit); -void rq_depth_scale_up(struct rq_depth *rqd); -void rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle); +bool rq_depth_scale_up(struct rq_depth *rqd); +bool rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle); bool rq_depth_calc_max_depth(struct rq_depth *rqd);
void rq_qos_cleanup(struct request_queue *, struct bio *); --- a/block/blk-wbt.c +++ b/block/blk-wbt.c @@ -307,7 +307,8 @@ static void calc_wb_limits(struct rq_wb
static void scale_up(struct rq_wb *rwb) { - rq_depth_scale_up(&rwb->rq_depth); + if (!rq_depth_scale_up(&rwb->rq_depth)) + return; calc_wb_limits(rwb); rwb->unknown_cnt = 0; rwb_wake_all(rwb); @@ -316,7 +317,8 @@ static void scale_up(struct rq_wb *rwb)
static void scale_down(struct rq_wb *rwb, bool hard_throttle) { - rq_depth_scale_down(&rwb->rq_depth, hard_throttle); + if (!rq_depth_scale_down(&rwb->rq_depth, hard_throttle)) + return; calc_wb_limits(rwb); rwb->unknown_cnt = 0; rwb_trace_step(rwb, "scale down");